ESE's works engine tuner

[F5 Dave]

Thought that was the case.

ahh, so there are 2ndries? I thought I had seen a GP with only main transfers. (bear in mind this was weeell over 10 years ago since I eyeballed one)

Or do you mean add ons as if someone had done it after? Are other GPs like this?

[TZ350]

Well, as you know, excessive heat in the combustion chamber is the primary cause of detonation. You have stated that the Piston is touching the head, now, applying just simple logic, now, as you have stated previously, there is "stretch" in the rod at high R.P.M (giving rise to the concept of "dynamic" cylinder compression ratio, now, I am putting forth the concept, that with the addition of this new "variable" of a Combustion chamber "liner" made of Copper (and copper expands quite dramatically with heat), your "dynamic cylinder compression ratio" is increasing with not only R.P.M, BUT ALSO TEMPERATURE!

There is no way the copper expands enough to affect the compresion ratio.

I used the term "Dynamic" in my earler calculations of compresion ratio to take account of the rod streach. Thats why the ratios given are labled "Dynamic.......at 10,000rpm".

Like you say, the rod streach and how it affects a staticly measured compresion ratio is something to bear in mind.
I figure on my engine the difference between the static and dynamic clearance volumes is about 1.25cc.

The dynamic stretch for my motor is about 0.5mm and I have got pretty good at shimming the barrel so the piston just kisses the head when I want it to. I would not normally do this as it puts the MSV out but I wanted to squeeze the compression a bit for the short track and the new head.

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[TZ350]

Thought that was the case.

ahh, so there are 2ndries? I thought I had seen a GP with only main transfers. (bear in mind this was weeell over 10 years ago since I eyeballed one)

Or do you mean add ons as if someone had done it after? Are other GPs like this?

No... done by the factory and I thought they were all like this. The barrel looks like it was originally meant to have the traditional 70's Suzuki two main transfers then the marketing people said Yamaha has four, so they add secondary’s fead from the main's, and ugly it is.


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[TZ350]

I forgot about your heatsink machined into a head idea, and I think it has merit!

Just to play devils advocate, I am no scientist, (and far from it), but does anyone know how good a heat sink is at expelling heat energy to the air? I am curious, as I appreciate they are good at drawing heat away from something, but what happens then?

But, the idea really has me interested. I would be VERY interested in the results.

Sadly the heat sink idea won't work, even a big block of aluminium would not work for my bike. You probably have already thought of the reason yourself. But I will draw a pic to explain why I don't think using a heat sink or a big block of aluminium is a flyer.

The sharp peak in the picture represents the fins, the sloping line "T" represents the thermal gradient, the bottom (X) axis is the distance from the fin to the combustion chamber and the (Y) axis "T" represents temperature.

The function of the heads cooling system is to cool the combustion chamber surface.

The roots of the fins on my GP125 head are very close, as close as you can get to the combustion chamber surface "C1 in the pic" and the heat-sink combustion chamber surface "C2 in the pic" is much further from its fins and so the thermal resistance is greater and the combustion chamber surface of the heat-sink will run much hotter and be less responsive to changes in the thermal load.

A good head has a very short thermal path to the cooling system. That’s one of the reasons water cooling works so well. Air cooled heads suffer from a space problem, in trying to get sufficient fins close to the combustion chamber shell.

This is one reasion why those aero engines had such thin fins, its to pack them in.

Copper with twice the thermal conductivity or half the thermal slope (less heat resistance), looks like it could remove heat from the combustion chamber surface much more efficiently (quickly) than aluminium. This should be good for an aircooled motor or even a water cooled one if you needed too.

My conclusion:- The longer and/or steeper the thermal path to the cooling system (fins or water) the higher the temperature, will be of the combustion chamber surface!

So big heat-sinks and big blocks of aluminium are non-starters which is a pity. The only way to improve the air-cooled head is to get more or better fins closer to the combustion chamber shell. Hence the oversized copper head gasket that is also a large fin.

Works a treat!

Now to reduce the heat uptake in the exhaust and then we can work on the scavenge patterns for more and better power.

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[saxet]

[QUOTE=F5 Dave;1994293]Thought that was the case.

ahh, so there are 2ndries? I thought I had seen a GP with only main transfers.

I've seen a few GP barrels of late and they are as TZ describes.

[speedpro]

Both my MBs have the transfers closest to the exhaust port at a greater angle up the bore than the rear transfers which are themselves angled up. By contrast my earlier engines had the main transfers angled flat across the piston. I thought Wobbly had made a mistake when he wrote the numbers down so I checked.

Interesting little ramp on the base of the transfers in the picture from SS90.

[Chambers]

Yea, I have to agree, I worded that incorrectly. sorry abouot that. Your "on the ground", I'm on the other side of the world. I'm not calling you a liar, but can you take a clear picture of the crown for me, I am really confident I can see detonation....Trust me, I have seen alot in my time! DOH!

You can take a good picture but by the time Kiwi Biker compacts it to size it loses a lot of definition.

There is half a chance TZ is familiar with what end gas detonation in the squish zone looks like.

Its the reason they put those bronze inserts there. Although bronze is not a very good thermal conductor compaired to aluminum it is used for its wear resistant properties, and to repair existing detonation damage, as they don't get eroded like aluminum does.

Just ask TZ.

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[Chambers]

Both my MBs have the transfers closest to the exhaust port at a greater angle up the bore than the rear transfers which are themselves angled up. By contrast my earlier engines had the main transfers angled flat across the piston. I thought Wobbly had made a mistake when he wrote the numbers down so I checked.

Interesting little ramp on the base of the transfers in the picture from SS90.

The primaries steeper than the secondarys, I have never seen that before could you show us a sketch of them?
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[TZ350]

Sorry SS90, I kept calling them "Janti" but they are "Jante" patterns.

An Extended Jante Test Procedure for Two-Stroke Piston-Ported Engine Development
Document Number: 941679

Date Published: September 1994

Author(s):
Dennis W. Montville
Badih A. Jawad

Abstract:
Two-stroke engine development has been occurring for many years. One of the main criteria affecting two-stroke piston-ported engine performance is scavenging, which is the process of using the incoming fresh air charge to purge the cylinder of exhaust gases. Among the simplest test procedures employed to model scavenging air flow is the "Jante" test, developed by Alfred Jante. This test was developed primarily to develop port designs for engines operating at peak power and so gives results having limited use for engines operating over a wide range. By altering the operating procedure as discussed in this paper, the Jante test can be used to provide useful information about the engine's scavenging characteristics over a wider range of engine operation. This offers a powerful tool for determining a porting design's effect on scavenging, and therefore engine performance

SAE paper:- https://shop.sae.org/technical/papers/941679

If I ever get my scanner to work I will see if I can scan the relavent pages from Dr John Dixon's book "The High Performance Two-Stroke Engine".
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[TZ350]

You can take a good picture but by the time Kiwi Biker compacts it to size it loses a lot of definition.

There is half a chance TZ is familiar with what end gas detonation in the squish zone looks like.

Its the reason they put those bronze inserts there. Although bronze is not a very good thermal conductor compaired to aluminum it is used for its wear resistant properties, and to repair existing detonation damage, as they don't get eroded like aluminum does.

Just ask TZ.

.

As well as the usual culprits of heat, ignition, compression there is the problem of mismatched squish angles between head and piston leaving a small area of gas trapped at the outer edge that gets over squished then explodes. Common problem on early TZ's

Yep, everything from the wild gnawing of rats to a mild sand blast at the edges.

As well as the usual culprits of heat, ignition, compression there is the problem of mismatched squish angles between head and piston leaving a small area of gas trapped at the outer edge that gets over squished then explodes. Common problem on early TZ's.

I am mindfull of this traped gas problem when I run the piston real close to the head.

If you think your getting light detonation look for the tell tale black pepper spots on the plug insulator. Then if you lift the head there may be a light sand blasted look on the piston in the squish zone . Heavier detonation will show up on the plug insulator as spots of aluminum blasted of the piston crown.

Yep seen a bit of it, mostly on other peoples bikes mind.
.

[SS90]

Sorry SS90, I kept calling them "Janti" but they are "Jante" patterns.

An Extended Jante Test Procedure for Two-Stroke Piston-Ported Engine Development
Document Number: 941679

Date Published: September 1994

Author(s):
Dennis W. Montville
Badih A. Jawad

Abstract:
Two-stroke engine development has been occurring for many years. One of the main criteria affecting two-stroke piston-ported engine performance is scavenging, which is the process of using the incoming fresh air charge to purge the cylinder of exhaust gases. Among the simplest test procedures employed to model scavenging air flow is the "Jante" test, developed by Alfred Jante. This test was developed primarily to develop port designs for engines operating at peak power and so gives results having limited use for engines operating over a wide range. By altering the operating procedure as discussed in this paper, the Jante test can be used to provide useful information about the engine's scavenging characteristics over a wider range of engine operation. This offers a powerful tool for determining a porting design's effect on scavenging, and therefore engine performance

SAE paper:- https://shop.sae.org/technical/papers/941679

If I ever get my scanner to work I will see if I can scan the relavent pages from Dr John Dixon's book "The High Performance Two-Stroke Engine".
.

That would be cool to read!

I am luck enough to have been able to do some design work with the rendering program "CATIA" (Certainly not on my own, with a suitably qualified operator) when I started looking into scavenge patterns, it really did open my eyes!

I had noticed that you had spelled it wrong, it made no difference, as it was clear to me what you where talking about!

[SS90]

So big heat-sinks and big blocks of aluminium are non-starters which is a pity. The only way to improve the air-cooled head is to get more or better fins closer to the combustion chamber shell. Hence the oversized copper head gasket that is also a large fin.

Works a treat!


.[/QUOTE]

Yea, I was doubting the idea of the heat-sink/big block of Aluminium concept a little, but the idea was really exciting to me.

I think your research has shown it is not really feasable. (Pity really)

Just looking at the differences in piston crown condition, (from an earlier post,which was regarding 4 point (piston /cylinder temp) related seizure marks), and comparing it to the last one you posted, I just see a totally different combustion chamber condition.

As you said, you have too much heat in your exhaust port area (I think, from the picture, as it's hard to tell (obviously), that this is evident by the colour of the crown on the exhaust side.

Now, obviously, due to the fact that you have such a large port time area, there is significant heat generated in this local area, but it is more pronounced on the second picture, and, the condition of the copper combustion chamber (to me) looks very "distressed"

Of course, having said that, I have never seen a copper combustion chamber insert of this type on any two stroke engine in my life, so how can I comment!

I have read a post that Fooman has made, and while he states a good case that my theory of the copper expanding and reducing the clearance further is wrong, I remain strong in that idea!

[SS90]

Why? Are you assuming that the copper insert expands into the combustion chamber? It won't. The insert is essentially a sheet with a hole in it. As the insert warms up, the hole becomes larger, unless it is sufficiently restrained by the shear force applied by the tension in the head bolts (in which case the insert will then have thermally induced stresses). Holes in things undergoing thermal expansion get bigger, not smaller.

There is a small mis-match in thermal expansion between aluminium-silicon casting alloys and copper alloys (copper doesn't expand as much, α = 21e-6 for Al-Si, 18e-6 for Cu), but the effect will be minor, especially given the mechanical restraint.

Cheers,
FM

O.K, you make a valid point.

I am still strong in my opinion though.

Way back (my first post), I talked about the idea of "wasted studs", and the reason they where used (pretty much all high performance engines, 2 stroke or other wise), since the 80's

The reason was to stop "cylinder crush"


I later gave an example of the first "Denco" built air cooled V-twin, suffering this problem, and wasted studs remedied it.

Could it be said the the "unwasted studs provided too much "mechanical restraint" (for the situation).....?????

It's generally accepted that a hot running air cooled engine will expand (if allowed by the studs expanding to do so) up to .5 of a millimeter (from room temperature, to "full heat" (or say Normal operating temperature in a racing engine)

If the studs ARE able to expand, I surmise that the "dynamic compression ratio" is somewhat less than if the expansion of the studs was not permissible (when you consider the stretch of the rod at high R.P.M is the cause of this increase.

If the studs are very thick, and do not allow this expansion, then something must give..... the outcome is usually the cylinder "squashing".

(being "pulled down", and therefore "out of round" as well.)

Now, here we have an engine, making much more power (and temperature) than was ever designed by the boys at Suzuki.

I am pretty sure that the cylinder is getting "squashed" (from other pics I have seen, as well as plenty of experience with such problems.)

Teezee even states he has a temperature problem in the exhaust area.... I suspect more now than with the aluminium only head!

(I haven't only been tuning scooters...... there was a selection process I went through to get this job!.... Experience and qualifications where mandatory)

I respect the figures you posted, and that's cool, but I just feel from what I see (and have experienced) that the copper is causing problems......

Again, I am not the "man on the ground"

If Teezee has the spare time, perhaps we can get some detailed pics?

[SS90]

Both my MBs have the transfers closest to the exhaust port at a greater angle up the bore than the rear transfers which are themselves angled up.

I think you could be on to something there!

[koba]

I don't think the idea that the copper expanding and tightening up the squish clearance sounds right but...

We know the copper absorbs and transfers heat better so could it be gettting really hot on the inside and acting as a bit of a glowplug?

There is debate over whether it is detonating or not but is the idea worth considering?